Many of today's televisions, whether analog or digital, provide for various sorts of graphics subdisplays that may be overlaid over the main video image. For example, many television signals carry closed caption information so that a subdisplay of alphanumeric characters can be overlaid at the bottom of the screen. As another example, other television accommodate "on-screen" subdisplays of user controlled options such as channel or volume.
In digital television systems, providing graphics subdisplays is accomplished by inserting the subdisplay data into the video data path. However, depending on the point of insertion, this can result in less than optimal image quality. For example, if the graphics data is inserted so that it undergoes the same processing as the main video data, it may lose resolution.